The present invention relates to certain enzyme inactivators which are especially useful for co-administration with other therapeutic compounds such as antiviral compounds in order to provide an improved therapeutic index by reducing the toxic side-effects.
A therapeutic nucleoside analogue that has been found to have a particularly beneficial clinical effect against a spectrum of conditions associated with Human Immunodeficiency Virus (HIV) infections such as Acquired Immune Deficiency Syndrome (AIDS), AIDS-related complex (ARC) and asymptotomatic infections, is the compound 3xe2x80x2-azido-3xe2x80x2-deoxythymidine having the approved name zidovudine. This compound at low doses is generally very well tolerated by patients and is now widely used in the treatment of HIV infections. However, in certain patients treated with zidovudine, some haematogical suppression including anaemia and neutropenia may be observed, presumably arising from a certain limited level of toxicity of zidovudine observed towards stem cells. Other less commonly observed side-effects have been described such as myopathy which may be related to intracellular activity of zidovudine.
It has now been found that the stem cell and haematological toxicity of zidovudine can be reduced by co-administration of an inactivator of the enzyme uracil reductase (dihydropyrimidine dehydrogenase, EC 1.3.1.2) which reduces the degradation of uracil.
The present invention is thus based on the discovery that the use of an inactivator of uracil reductase in combination with zidovudine reduces the cellular toxicity of zidovudine.
According to the present invention therefore we provide a uracil reductase inactivator for use in medical therapy, especially in combination with zidovudine or a pharmaceutically acceptable salt or ester thereof, for example in the treatment or prophylaxis of HIV infections such as AIDS, ARC and asymptomatic infections.
The present invention further provides:
a) a combination of a uracil reductase inactivator and zidovudine or a pharmaceutically acceptable salt or ester thereof;
b) a method for the treatment or prophylaxis of an HIV infection in a human which comprises administering to the said human an effective anti-HIV amount of zidovudine or a pharmaceutically acceptable salt or ester thereof in combination with a uracil reductase inactivator.
It should be noted that the references herein to uracil reductase inactivators refer to compounds that inactivate the uracil reductase enzyme, effectively acting as suicide substrates, in contrast to compounds that merely have an inhibiting effect on the enzyme.
It has been found that particularly beneficial effects in reducing the toxicity of zidovudine have been achieved using as a uracil reductase inactivator a 5-substituted uracil compound, particularly a uracil compound substituted in the 5-position by a halogen atom e.g. iodine or bromine; a C2-4 alkenyl group (e.g. vinyl) optionally substituted by halogen e.g. 2-bromovinyl, 1-chlorovinyl or 2-bromo-1-chlorovinyl; a C2-6 alkynyl group optionally substituted by a halogen (e.g. bromine) atom; a cyano group; or a C1-4 alkyl group substituted by halogen e.g. trifluoromethyl. Particularly preferred inactivators of uracil reductase for use in accordance with the invention are 5-ethynyluracil and 5-propynyluracil. Other inactivators for such use include:
5-ethynyluracil
5-cyanouracil
5-propynyluracil
5-bromoethynyluracil
5-(1-chlorovinyl)uracil
5-iodouracil
5-bromovinyluracil
5-hex-1-ynyluracil
5-vinyluracil
5-trifluorouracil
5-bromouracil
5-(2-bromo-1-chlorovinyl)uracil
In experiments in mice, it has been found that red-blood cell anaemia induced by treatment with zidovudine could be at least partially prevented by treatment with 5-ethynyluracil.
The above 5-propynyluracil is a novel compound and represents a further feature of the present invention.
Other uracil reductase inactivators which may be employed in accordance with the present invention include compounds which generate the above uracil compounds in vivo. Such compounds include nucleoside derivatives which contain a nucleobase corresponding to the above 5-substituted uracil compounds, for example nucleoside derivatives containing a ribose, 2xe2x80x2-deoxyribose, 2xe2x80x2,3xe2x80x2-dideoxyribose, arabinose or other cleavable sugar portion, which may additionally contain a 2xe2x80x2- or 3xe2x80x2-substituent such as halo, for example fluoro. Specific examples of such nucleoside derivatives are 1-(xcex2-D-arabinofuranosyl)-5-prop-1-ynyluracil and 2xe2x80x2,3xe2x80x2,-dideoxy-5-ethynyl-3xe2x80x2-fluorouridine.
Zidovudine or a pharmaceutically acceptable salt or ester thereof and the said uracil reductase inactivator may be employed in combination in accordance with the invention by administration of the components of the combination to an appropriate subject either concomitantly, for example in a unitary pharmaceutical formulation, or, more preferably, separately, or sequentially within a sufficient time period whereby the desired therapeutic effect of the combination is achieved.
Zidovudine or a pharmaceutically acceptable salt or ester thereof and the uracil reductase inactivator may be administered respectively for therapy by any suitable route including oral, rectal, nasal, topical (including buccal and sublingual), vaginal and parenteral (including subcutaneous, intramuscular, intravenous and intradermal); the oral route is especially preferred. It will be appreciated that the preferred route will vary with the condition and age of the recipient, the nature of the infection and other clinical factors.
In general a suitable dose of zidovudine or a pharmaceutically acceptable salt or ester thereof will be in the range of 1.0 to 120 mg per kilogram body weight of the recipient per day, preferably in the range of 2 to 30 mg per kilogram body weight per day and most preferably in the range of 5 to 20 mg per kilogram body weight per day. The desired dose is preferably presented as two, three, four, five, six or more sub-doses administered at appropriate intervals throught the day. These sub-doses may be administered in unit dosage forms, for example, containing 10 to 1500 mg, preferably 20 to 1000 mg, and most preferably 50 to 700 mg of active ingredient per unit dosage form.
Experiments with 3xe2x80x2-azido-3xe2x80x2-deoxythymidine suggest that a dose should be administered to achieve peak plasma concentrations of the active compound of from about 1 to about 75 xcexcM, preferably about 2 to 50 xcexcM, most preferably about 3 to about 30 xcexcM. This may be achieved, for example, by the intravenous injection of a 0.1 to 5% solution of the active ingredient, optionally in saline, or orally administered as a bolus containing about 1 to about 100 mg/kg of the active ingredient. Desirable blood levels may be maintained by a continuous infusion to provide about 0.01 to about 5.0 mg/kg/hour or by intermittent infusions containing about 0.4 to about 15 mg/kg of the active ingredient.
The uracil reductase inactivator may be administered in a dosage in the range of 0.01 to 50 mg per kilogram body weight of the recipient per day, preferably in the range of 0.01 to 10 mg per kilogram body weight per day, most preferably in the range of 0.01 to 0.4 mg per kilogram body weight per day; an alternative preferred administration regime is 0.5 to 10 mg/kg once per week.
The desired dose is preferably presented as one, two or more sub-doses administered at appropriate intervals throughout the day. These sub-doses may be administered in unit dosage forms for example containing 1 to 200 mg, preferably 2 to 100 mg, most preferably 2 to 50 mg of the uracil reductase inactivator.
Zidovudine and the uracil reductase inactivator are employed in an appropriate ratio whereby the above-mentioned toxic effects of zidovudine are reduced or obviated without significant reduction of the therapeutic effect of zidovudine; such a ratio (based on the respective weights of zidovudine and uracil reductase inactivator) is generally in the range 1:1 to 1000:1, preferably in the range 5:1 to 500:1 and particularly in the range 20:1 to 200:1.
Zidovudine and the uracil reductase inactivator are preferably administered in a pharmaceutical formulation, either in a single pharmaceutical formulation containing both components or in separate pharmaceutical formulations each containing one of the components of the combinations.
The present invention thus includes as a further feature a pharmaceutical formulation comprising a uracil reductase inactivator optionally in combination with zidovudine or a pharmaceutically acceptable salt or ester thereof together with at least one pharmaceutically acceptable carrier or excipient.
Each carrier must be xe2x80x9cpharmaceutically acceptablexe2x80x9d in the sense of being compatible with the other ingredients of the formulation and not injurious to the patient. Formulations include those adapted for oral, rectal, nasal, topical (including buccal and sublingual), vaginal and parenteral (including subcutaneous, intramuscular, intravenous and intradermal) administration. The formulations may conveniently be presented in unit dosage form and may be prepared by any methods well known in the art of pharmacy. Such methods include the step of bringing into association the active ingredient with the carrier which constitutes one or more accessory ingredients. In general, the formulations are prepared by uniformly and intimately bringing into association the active ingredient with liquid carriers or finely divided solid carriers or both, and then if necessary shaping the product.
Formulations of the present invention adapted for oral administration may be presented as discrete units such as capsules, cachets or tablets each containing a predetermined amount of the active ingredient; as a powder or granules; as a solution or a suspension in an aqueous (at pH 10) or non-aqueous liquid; or as an oil-in-water liquid emulsion or a water-in-oil liquid emulsion. The active ingredient may also be presented as a bolus, electuary or paste.
A tablet may be made by compression or moulding, optionally with one or more accessory ingredients. Compressed tablets may be prepared by compressing in a suitable machine the active ingredient in a free-flowing form such as a powder or granules, optionally mixed with a binder (e.g. povidone, gelatin, hydroxypropylmethylcellulose), lubricant, inert diluent, preservative, disintegrant (eg. sodium starch glycollate, cross-linked povidone, cross-linked sodium carboxymethylcellulose) surface-active or dispersins agent. Moulded tablets may be made by moulding in a suitable machine a mixture of the powdered compound moistened with an inert liquid diluent. The tablets may optionally be coated or scored and may be formulated so as to provide controlled release of the active ingredient therein using, for example, hydroxypropylmethyl cellulose in varying proportions to provide the desired release profile.
Formulations for topical administration in the mouth include lozenges comprising the active ingredient in a flavoured basis, usually sucrose and acacia or tragacanth; pastilles comprising the active ingredient in an inert basis such as gelatin and glycerin, or sucrose and acacia; and mouthwashes comprising the active ingredient in a suitable liquid carrier.
Formulations for rectal administration may be presented as a suppository with a suitable base comprising for example cocoa butter or a salicylate.
Formulation for vaginal administration may be presented as pessaries, tampons, creams, gels, pastes, foams or spray formulations containing in addition to the active ingredient such carriers as are known in the art to be appropriate.
Formulations for parenteral administration include aqueous (at pH 10) and non-aqueous isotonic sterile injection solutions which may contain anti-oxidants, buffers, bacteriostats and solutes which render the formulation isotonic with the blood of the intended recipient; and aqueous and non-aqueous sterile suspensions which may include suspending agents and thickening agents. The formulations may be presented in unit-dose or multi-dose sealed containers, for example, ampoules and vials, and may be stored in a freeze-dried (lyophilized) condition requiring only the addition of the sterile liquid carrier, for example water for injections, immediately prior to use. Extemporaneous injection solutions and suspensions may be prepared from sterile powders, granules and tablets of the kind previously described.
Preferred unit dosage formulations are those containing a daily dose or unit, daily sub-dose, as herein above recited, or an appropriate fraction thereof, of an active ingredient.
The above-mentioned uracil reductase inactivators which are employed in combination with zidovudine in accordance with the present invention may be prepared in conventional manner. For example, the inactivators referred to above may be prepared by the methods described in J. Heterocycl. Chem. 19(3) 463-4 (1982) for the preparation of 5-ethynyluracil; J. Chem. Soc. Perkin Trans. 1(16), 1665-70 (1981) for the preparation of 5-(2-bromovinyl)uracil, 5-bromoethynyluracil and 5-(2-bromo-1-chlorovinyl)uracil; Nucleic Acid Chemistry, Vol. 2, 927-30 (1978) for the preparation 5-cyanouracil; Nucleic Acids Research, 1(1) 105-7 (1974) for the preparation of 5-vinyluracil; Z. Chem. 17(11) 415-16 (1977) for the preparation of 5-trifluoromethyluracil; Nucleic Acids Research 3 (10), 2845 (1976) for the preparation of 5-(1-chlorovinyl)uracil.
The above nucleoside derivatives may also be prepared in conventional manner, for example in accordance with processes described in European Patent Specification No. 356166 for the preparation of 3xe2x80x2-fluoro-2xe2x80x2, 3xe2x80x2-dideoxy-5-alkynyluridine compounds, such as 2xe2x80x2,3xe2x80x2-dideoxy-5-ethynyl-3xe2x80x2-fluorouridine, and European Patent Specification No. 272065 for the preparation of 5-alkynyluracil arabinosides, such as 1(xcex2-D-arabinofuranosyl)-5-prop-1-ynyluracil.
The novel 5-propynyluracil compound referred to above may be prepared by one of the following processes, namely:
a) treatment of a 5-propynyluridine compound to effect conversion thereof to the desired uracil compound; or
b) treatment of a uracil compound substituted in the 5-position by an appropriate leaving group with a propyne compound to give the desired uracil compound.
In the above process a), conversion may be effected by enzymatic means, for example by treatment of the uridine compound with a thymidine phosphorylase enzyme, advantageously in a buffered medium at a pH of 6 to 8.
In the above process b), a uracil compound substituted in the 5-position by a suitable leaving group e.g. iodo or bromo, is treated with a C3-6 alkyne in the presence of an appropriate palladium catalyst such as bis (triphenylphosphine) palladium (II) chloride and cuprous iodide in an amine solvent such as triethylamine.
Other 5-substituted uracil compounds for use in accordance with the invention may be prepared in an analogous manner to those described above.
The following Examples illustrate the present invention.